The pilot was landing on a gravel runway as part of a organized fly-in event. During the landing roll an all-terrain vehicle (ATV) entered, and proceeded down the runway weaving from side-to-side. In an attempt to avoid the ATV he pulled back on the control yoke, and climbed the airplane over the ATV. The airplane drifted to the left, and struck a tree on the edge of the runway; it then turned left 180 degrees, and came to rest in the brush alongside the runway. The airplane sustained substantial damage to the right aileron. In the pilot’s written statement to the National Transportation Safety Board he noted that the accident might have been avoided if organizations which host these type of events took responsibility for securing the runway.